Upload & Sell: Off
Any social media for that matter, not just Facebook. Common sense really. If you have important work that needs to be viewed it should reside behind a password protected folder on your own website.
Well, yes. And, no.
This is a social media site, too. ;-)
There are two extreme notions about how to deal with the issues that are coming up in this thread:
1. Put everything out there in full, high-defintion form with no watermarks, copyright notices, or other embedded imagery or even file content - strip out that EXIF. It is a whole new world. Content wants to be free. GIve it away.
2. Keep everything locked up. Never share any files on the net or in digital form. Don't share your work except as prints.
While I can imagine a few unusual cases in which either of those extreme approaches might make sense, neither will work well for most people. In the end it is a question of balancing the potential risks of sharing with the potential gains of sharing, and then finding an appropriate path through all of this stuff that provides, for you, the best balance of lowered risk and reasonable gain.
It is absolutely true that if you share anything on the internet, it can be repurposed and used in some way that you did not authorize. Someone will make a desktop image out of it or put it on their web site or perhaps include it in a printed version of their holiday card or... you get the picture. These are risks.
At the same time, there are benefits to sharing your work (and your story and perhaps your knowledge and opinions) on the internet that might be enough to make the risks worthwhile, at least if you can limit those risks to some extent. You might think that having people see and enjoy your work is sufficient reward, or you might be interested in the beneficial effect on your "brand" that can come from having your work seen and talked about.
So, what balance is right? This is a distinctly personal question, and the answer depends upon what gains your hope for and what risks you fear and how much. For many, the loss that would come from not being present at all in the online world makes the idea of locking everything up on the hard drive a poor choice from just about every perspective, including a business perspective and even from an intellectual property rights point of view. Yet, the potential risks that may come from sharing full-size, high resolution, unmarked image files are not worth the potential for gain that can come from sharing.
So a compromise is usually necessary. For many it takes the form of releasing only relatively small, medium or low quality jpg files, incorporating copyright information, branding text, and watermarks. Even here there is some risk - a dedicated bad guy could remove the identifying file and image information and perhaps use the resulting image as a web page spot image or perhaps as a cell phone desktop. But most people who would do such a thing will look elsewhere for images that easier pickings - bigger, higher quality, no test to remove.
There is another issue though, that is a larger one than simple photo sharing. That is the increasing tendency to give our means of communication, the storage and sharing of our electronic property, and our personal information over to large corporate entities who then, more and more, take control of our property and our lives and the means of communication. I'm not happy to see the number of people who now prefer to communicate via Facebook messaging rather than regular old universally readable and public domain format email. I'm concerned about people whose entire online presence is via services such as Facebook or Flickr or similar. The original power of the web came largely because it was not proprietary - the standards were open and available to all, and users controlled their own content. Heck, it wasn't even that hard to run your own server - such capabilities were built into a number of OS's.
I think we are a bit to blithe about turning ourselves, our content, and more over to social media services... apparently just because the financial cost seems so small.